Linear space-time precoding for OFDM systems based on long-term CSI

This paper addresses the severe performance degradation for OFDM systems in case of long channel delays exceeding a guard interval. Such long delays can be seen as an interference source on one hand and also as a valuable frequency diversity source on the other hand. Instead of simply suppressing such long delays, e.g. by beamforming at transmitter, the newly proposed preceding scheme attempts to find the optimum trade-off between the interference suppression and the diversity gain for the long delays. The optimization problem is formulated exploiting only long-term channel state information instead of the instantaneous one and it is solved based on the minimum mean square error criterion with a constraint on the transmit power. Computer simulation results show that the proposed scheme outperforms the conventional beamforming scheme.